Air supply facilities for air spring facilities or other applications in a vehicle produce compressed air in order to feed it to an air spring facility, for example. The compressed air is produced by means of a compressor element, which is driven by an electric motor. A DC motor with brushes is generally used as an electric motor for this purpose. In the onboard electrical system of the vehicle, especially a motor car, this motor is supplied with electrical energy from a battery. Such batteries have an electrical voltage across the terminals in the range of from 9 to 15 V, for example. The voltage amplitude depends especially on the current loading of the battery and on its state of charge.
To operate the electric motor of a compressor, it can be connected electrically to the battery by means of a relay. The voltage of 9 V to 15 V, to remain with the example, is then applied to the motor and the motor is driven thereby. As the motor starts up, a very high starting current can occur, and this also leads to at least a temporary voltage drop in the battery. The operation of other loads in the onboard electrical system, especially the starting up of other loads in the onboard electrical system, can likewise lower the battery voltage, and the switching off of such a load can raise the battery voltage again. Such fluctuating voltages in the battery lead to different currents, which, in turn, can lead to suboptimal operating conditions and, for example, increased brush wear in the electric motor. Moreover the result is different speeds of the electric motor and hence of the compressor element, which can lead to differences in the noise generated. In particular, it is difficult to match soundproofing to a predetermined noise frequency.
A brushless electric motor is known from CN201794753U, for example. In principle, an electrically commutated brushless motor is constructed as a DC motor having a power electronics unit (“BLDC motor”). The winding is generally mounted on the stator, not in the rotor (as in the DC motor with brushes); in the case of the BLDC motor, the mechanical commutator or brush system is replaced by an electronic commutator, namely a “BLDC control circuit” for controlling a drive of the motor. In general, permanent magnets are seated in the rotor for permanent excitation. A control circuit with the power electronics unit can switch the DC supply voltage to the motor windings. Most BLDC motors have three windings, which are arranged in a star shape. By means of pulse width modulation (PWM), the control circuit can change the average voltage to the motor, for example, in order to control the rotational speed. Hall-effect sensors, for example, which are embedded in the stator, can measure the angular position of the rotor. When the rotor magnet poles then pass the Hall-effect sensors, they emit a high or low signal, thereby indicating whether this is a north or a south pole. BLDC motors can also be commutated by monitoring the back EMF signals instead of using Hall-effect sensors. The motor is then started in an open circuit, and the control then switches to the sensing of the back EMF. However, there is generally a limitation to applications with a relatively constant torque and without dynamic requirements.
DE 10 2007 042 318 A1 describes a compressor arrangement of the general type under consideration having a compact dry piston compressor having at least one cylinder for compressing air of an associated piston, which can be moved using an electric motor by a crank mechanism consisting of a crankshaft and a connecting rod. For this purpose, the crank mechanism is accommodated in a first half of a housing, and the electric motor is accommodated within a second half of the housing. A rolling bearing common to the crank mechanism and to the electric motor is inserted in a dividing wall dividing the housing halves. The electric motor is embodied in the manner of a brushless DC motor, the stator of which consists of coil windings with an iron core and the rotor of which is equipped with permanent magnets. An electronic commutator of the electric motor is arranged on a circuit board accommodated in the second housing half. The electric motor, which is designed as an internal rotor motor, can have a rotor formed integrally with the crankshaft, which is rotatable within the stator. A compressor arrangement of this kind is capable of further improvements as regards control and structural design.
A pneumatic facility of the general type under consideration is constructed, in particular, in the form of a pneumatic spring system of a vehicle, which is operated using a compressed air supply facility.
A compressed air supply facility is used in vehicles of all kinds, especially to supply an air spring facility of a vehicle with compressed air. Air spring facilities can also include leveling devices, by means of which the distance between the vehicle axle and the vehicle body can be adjusted. An air spring facility of a pneumatic system comprises a number of pneumatic bellows pneumatically connected to a common line (gallery), which can raise the vehicle body as the compressed air charge increases—also referred to as air admission—and can correspondingly lower the vehicle body as the compressed air charge decreases—also referred to as venting. In this case, there is generally a need for compressed air flows at pressures of up to 20 bar or above. With increasing distance between the vehicle axle and the vehicle body or ground clearance, the spring travels become longer and it is also possible to compensate for larger irregularities in the ground without contact with the vehicle body. Such systems are increasingly being used for preference in all-terrain vehicles and sport utility vehicles (SUV). In the case of very powerful engines, especially in SUVs, it is desirable to provide the vehicle with a relatively small ground clearance for high speeds on the road, on the one hand, and to provide it with a relatively large ground clearance for off-road use, on the other. It is furthermore desirable to implement a change in the ground clearance as quickly as possible, something that increases the demands as regards rapidity, flexibility and reliability of a compressed air supply facility, especially also that of a compressor arrangement. Nevertheless, this should involve as little wear as possible and be as robust and compact as possible and, in particular, should meet the installation space requirements in a vehicle.
In order to ensure long-term operation of the compressed air supply facility, a pneumatic main line of the compressed air supply facility has an air dryer, by means of which the compressed air can be dried. Accumulation of moisture in the pneumatic system is thereby avoided. At relatively low temperatures, moisture can lead to crystal formation, which damages valves, and can furthermore lead to unwanted effects in the compressed air supply facility and in the pneumatic facility. An air dryer has a desiccant, usually granules, through which the compressed air can flow, allowing the granules to remove moisture contained in the compressed air by adsorption. If appropriate, an air dryer can be designed as a regenerative air dryer. In this case, the dried compressed air from the pneumatic facility, in particular an air spring facility, is made to flow through the granules during each venting cycle, usually as a countercurrent but, depending on the design, possibly also as a co-current relative to the air admission direction. Regeneration of the air dryer is made possible essentially by a pressure change at the air dryer, wherein a pressure present during regeneration, as compared with that for adsorption, is as a rule lower in order to allow release of moisture from the granules. For this purpose, the vent valve arrangement can be opened, wherein the regenerability of the air dryer is generally dependent on the pressure conditions and the pressure change amplitude in the compressed air supply facility. For “pressure change adsorption” of this kind too, it has proven desirable to make a compressed air supply facility flexible and, at the same time, reliable. In particular, the aim is, on the one hand, to allow relatively quick venting, while a sufficiently high pressure change amplitude at a low air pressure—i.e., during regeneration—should nevertheless be available for regeneration of the air dryer.
It is desirable to adapt a compressed air supply facility to the requirements of a vehicle in a manner that is as advantageous as possible; this applies to a pneumatic, structural and/or electrical and/or electronic configuration thereof—in particular, it applies to a compressor arrangement for operating the compressed air supply facility.